1. Field of the Invention
This invention relates to tongue plate devices for use in seat belts provided in a vehicle for restraining occupants to seats of the vehicle to ensure the restraining effect to the occupants in an emergency, and more particularly to a tongue plate device for use in a seat belt system of a kind using a continuous webbing consisting of a lap belt and a shoulder belt.
2. Description of the Prior Art
A three-point type safety seat belt system using a continuous webbing consisting of a lap portion and a shoulder portion is recently widely employed in vehicles.
A typical form of prior art tongue plate devices widely employed in the seat belt systems of this kind is generally constituted by a single member which is provided at one end thereof with an opening adapted to be engaged by a buckle and at the other end thereof with another opening adapted to permit passage of the continuous webbing therethrough.
The structure of the prior art tongue plate device has been such that the webbing passing opening provides a resistance against the webbing passing therethrough and this resistance is utilized to bear the force opposing to the retracting force of the seat belt retractor and to prevent impartation of a tension to a part of the webbing passed already to the other side of the webbing passing opening thereby eliminating impartation of a sense of oppression to the occupant wearing the seat belt on his body.
However, due to the fact that such a resistance is not great enough to completely lock the webbing against passing movement through the webbing passing opening of the tongue plate device, an undesirable situation has been frequently given rise to in which the tongue plate device is displaced from the proper set position on the webbing during the use of the seat belt system or during the retracting movement of the webbing into the retractor or the seat belt is not properly fitted on the body of the occupant. Occurrence of such situation has resulted in an undesirable reduction of the effect of sufficiently restraining the wearer to the seat of the vehicle to ensure the safety of the wearer in case of emergency.
Further, the prior art tongue plate device constructed to provide such resistance has been defective in that this resistance provides an adverse effect of giving the occupant extreme inconvenience when he wears the seat belt on his body and when he tries to adjust the length of the seat belt.